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bloating in stoneware

updated fri 25 jun 04

 

Ron Roy on tue 15 jun 04


Hi Sarah,

I have never had the problem with stoneware or porcelain but I have seen it
with porcelain.

The first step for me would be to test your clay for absorbency - let me
know if you need to know how to do that.

Bloating is hard to define but there are several kinds - one which looks
like there was air in the clay - blisters but of different sizes and
randomly situated on the ware and can happen for 3 reasons - air in the
clay, improper bisque firing and improper mixing of the wet clay.

Could it be - when your remix is slaking - that some material in the clay
is collecting together and over fluxing the clay around it? You might be
able to see this if you look closely - with a magnifying glass - any
crystals from say solubles in the clay?

The 4th kind is called blebbing - the clay is overfired and blisters are
all over the ware - evenly spaced.

What kind are yours.

RR

>I have been having some bloating problems with my stoneware clay. A post
>about two weeks ago that mentioned bloating in porcelain attributed the
>problem to the recycling process. With that information I threw about 50 lbs
>of unpugged and unrecycled clay. I had very few bloats overall in the latest
>load (just fate making sure that I had nothing to compare to) But there were
>no bloats at all in the fresh clay.
>
>My current method is to let trimming scraps dry completely, then cover with
>water and throwing scrap and let it sit for a couple of days then pour and
>siphon water off the top. When it has settled and thickened enough I spoon
>it onto plaster bats. Then I pug it in with fresh clay.
>
>So now I need some suggestions on how to recycle scraps without getting
>bloats?
>
>Sarah House
>
>http://www.skhpottery.com
>
>In Little Switzerland, NC

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513

David Beumee on tue 15 jun 04


According to Dr. Carty at Alfred, his possible explanation for bloating in recycled clay may be associated with "surface dissolution and substitution in the flux particles." His suggestion to me is to slake for the shortest possible time and use an energetic mixer to accelerate the mixing process. I am now slaking and soaking small amounts of scrap for increasing amounts of time to find out at what soak time bloats appear upon firing. So, jury's out on why these bloats appear in the recycled clay only, but with Dr. Carty's theory and my work perhaps we'll be able to report some success in the near future.

David Beumee
Earth Alchemy Pottery
Lafayette, CO


> I have been having some bloating problems with my stoneware clay. A post
> about two weeks ago that mentioned bloating in porcelain attributed the
> problem to the recycling process. With that information I threw about 50 lbs
> of unpugged and unrecycled clay. I had very few bloats overall in the latest
> load (just fate making sure that I had nothing to compare to) But there were
> no bloats at all in the fresh clay.
>
> My current method is to let trimming scraps dry completely, then cover with
> water and throwing scrap and let it sit for a couple of days then pour and
> siphon water off the top. When it has settled and thickened enough I spoon
> it onto plaster bats. Then I pug it in with fresh clay.
>
> So now I need some suggestions on how to recycle scraps without getting
> bloats?
>
> Sarah House
>
> http://www.skhpottery.com
>
> In Little Switzerland, NC
>
> (soon to be Burnsville, NC)
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.

Carolynn Palmer on tue 15 jun 04


In a message dated 15/6/04 8:59:23 AM, sarah@SKHPOTTERY.COM writes:

<< Then I pug it in with fresh clay.

So now I need some suggestions on how to recycle scraps without getting
bloats?
>>

I'd skip that step: "Then I pug it in with fresh clay." - try just pugging
the recycled clay by itself. You are essentially mixing two very different
clays together when you add the fresh clay.
-Carolynn Palmer,
Somerset Center, Michigan

Paul B on tue 15 jun 04


On Laguna's website, click "support" and then the first article listed (as
of today) is about bloating and black coring, and i believe the info there
is accurate. A long time ago i was getting some bloating with bmix when i
only had an electric kiln (^10). In that case, the body may have had
something to do with it but is was more likely due to poor air circulation
in the kiln and also not firing the bisque hot enough (^06).
Now i use a stoneware i mix myself, and i bisque to ^04 (electric) and fire
glazes in a gas kiln, and never get any bloats at all, not even once, and i
reclaim a lot of clay. So i don't know that it matters whether one is
reclaiming clay (although there are many others on this list with more
experience than me who may say otherwise) but my guess is that the bisque
may not be hot enough. The article has more to say.
Paul B

sdr on tue 15 jun 04


We are really fortunate to have people like David
Beumee, willing to investigate all kinds of technical
issues that many can't or won't, and then share information
with the list.

Thanks, David - I've been following this bloating issue
with interest. I've not had the problem, but I'm starting
to recycle more porcelain, and I'm watching to see.....

regards

Dannon Rhudy
----- Original Message -----
From: "David Beumee"
To:
Sent: Tuesday, June 15, 2004 11:18 AM
Subject: Re: Bloating in stoneware


> According to Dr. Carty at Alfred, his possible explanation for bloating in
recycled clay may be associated with "surface dissolution and substitution
in the flux particles." His suggestion to me is to slake for the shortest
possible time and use an energetic mixer to accelerate the mixing process. I
am now slaking and soaking small amounts of scrap for increasing amounts of
time to find out at what soak time bloats appear upon firing. So, jury's out
on why these bloats appear in the recycled clay only, but with Dr. Carty's
theory and my work perhaps we'll be able to report some success in the near
future.
>
> David Beumee
> Earth Alchemy Pottery
> Lafayette, CO
>
>
> > I have been having some bloating problems with my stoneware clay. A post
> > about two weeks ago that mentioned bloating in porcelain attributed the
> > problem to the recycling process. With that information I threw about 50
lbs
> > of unpugged and unrecycled clay. I had very few bloats overall in the
latest
> > load (just fate making sure that I had nothing to compare to) But there
were
> > no bloats at all in the fresh clay.
> >
> > My current method is to let trimming scraps dry completely, then cover
with
> > water and throwing scrap and let it sit for a couple of days then pour
and
> > siphon water off the top. When it has settled and thickened enough I
spoon
> > it onto plaster bats. Then I pug it in with fresh clay.
> >
> > So now I need some suggestions on how to recycle scraps without getting
> > bloats?
> >
> > Sarah House
> >
> > http://www.skhpottery.com
> >
> > In Little Switzerland, NC
> >
> > (soon to be Burnsville, NC)
> >
> >
____________________________________________________________________________
__
> > Send postings to clayart@lsv.ceramics.org
> >
> > You may look at the archives for the list or change your subscription
> > settings from http://www.ceramics.org/clayart/
> >
> > Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>

Ivor and Olive Lewis on wed 16 jun 04


Dear David Beumee,
Accepting that Prof. Carty is on the right track here, how does his
theory account for the generation of a gas under relatively high
pressure that would distort the surface?
Does your original recipe for the clay have any substances in it that
might be responsible ; Do you add Calcium or Barium Carbonate, the one
to act as a supplementary flux, the other to overcome efflorescence of
soluble salts. Either of these would release Carbon dioxide. Are you
adding Epsom Salts to improve plasticity? Is there an appreciable
percentage of Iron in any of the clays in the body you are using?
Knowing that we can all suffer from this scourge It would be good to
know what the answer is.
Best regards,
Ivor Lewis. Redhill, South Australia

Sarah@skhpottery.com on wed 16 jun 04


I have been having some bloating problems with my stoneware clay. A post
about two weeks ago that mentioned bloating in porcelain attributed the
problem to the recycling process. With that information I threw about 50 lbs
of unpugged and unrecycled clay. I had very few bloats overall in the latest
load (just fate making sure that I had nothing to compare to) But there were
no bloats at all in the fresh clay.

My current method is to let trimming scraps dry completely, then cover with
water and throwing scrap and let it sit for a couple of days then pour and
siphon water off the top. When it has settled and thickened enough I spoon
it onto plaster bats. Then I pug it in with fresh clay.

So now I need some suggestions on how to recycle scraps without getting
bloats?

Sarah House

http://www.skhpottery.com

In Little Switzerland, NC

(soon to be Burnsville, NC)

David Beumee on wed 16 jun 04


Ivor wrote:
how does his
> theory account for the generation of a gas under relatively high
> pressure that would distort the surface?

I don't know. Dr. Carty's theory is that water may be contributing to the tiny bloating event, due to water attack on feldspar (or nepheline syenite) particles by allowing an ion exchange to occur between H30+ ions in the water and Na+ or K+ in the feldspar.

> Does your original recipe for the clay have any substances in it that
> might be responsible ; Do you add Calcium or Barium Carbonate, the one
> to act as a supplementary flux, the other to overcome efflorescence of
> soluble salts. Either of these would release Carbon dioxide.

Unfortunately, the original recipe is made commercially and is therefore proprietary information, but I will certainly retain your statement for future reference.

Are you
> adding Epsom Salts to improve plasticity? Is there an appreciable
> percentage of Iron in any of the clays in the body you are using?

I don't know if the manufacturer is adding Epsom salts to the body. I would be very surprised to find out they do. It is a porcelain body and I do know that no iron bearing clays are added to the recipe.

> Knowing that we can all suffer from this scourge It would be good to
> know what the answer is.

Yes indeed! Dr. Carty has also acknowledged that the problem is global. I am very excited to have a direction in which to carry out research.

David Beumee
Earth Alchemy Pottery
Lafayette, CO


> Dear David Beumee,
> Accepting that Prof. Carty is on the right track here, how does his
> theory account for the generation of a gas under relatively high
> pressure that would distort the surface?
> Does your original recipe for the clay have any substances in it that
> might be responsible ; Do you add Calcium or Barium Carbonate, the one
> to act as a supplementary flux, the other to overcome efflorescence of
> soluble salts. Either of these would release Carbon dioxide. Are you
> adding Epsom Salts to improve plasticity? Is there an appreciable
> percentage of Iron in any of the clays in the body you are using?
> Knowing that we can all suffer from this scourge It would be good to
> know what the answer is.
> Best regards,
> Ivor Lewis. Redhill, South Australia
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.

Jim Murphy on thu 17 jun 04


Hi all,

The work out of Alfred Univ. (Dr. Carty) - some of which was presented at
NCECA 2002 - indicates bloating is due to "gas bubble expansion" and there
appear to be TWO means via which bloating typically occurs:

1. Bloating due to Water - uneven drying and/or rapid steam generation
during early stages of firing.

2. Bloating due to over-firing - Viscosity (resistance-to-flow) of the
glass phase is too low to resist pressure within pores. This form of
bloating is evidenced by the formation of spherical pores.
[Note - "glass phase" here - I believe - refers to the typically
high-alkali
molten liquid formed, in part, from feldspar particles during firing]

I believe the suggestions to David Beumee regarding recycling clay &
clay-trimmings via short slaking-time and high-energy mixing would be
associated more-so with Item 2 above.

Why ? - Presumably, here the claybody constituents are "unknown" and the
water is "uncontrolled", i.e., NOT Reverse Osmosis (RO) and Deionized (DI)
water. (There may be "things" in your uncontrolled water - good or bad -
depending on your perspective.)

Short slaking-time, in theory, may help to limit the dissolution of
"residual elements", alkali-related things like divalent cations Ca2+, Mg2+,
etc. - either from the "uncontrolled slaking-water"-to-the-"unknown
clay/trimmings" or from the "unknown clay/trimmings"-to-the-"uncontrolled
slaking-water". (Less slaking-time MAY equal less dissolution)

Changes to alkali levels may affect melting characteristics and behavior,
i.e., "viscosity". In general terms, a higher-alkali molten liquid is less
viscous (less resistant to flow) and therefore it would be "easier" for gas
bubbles during firing to expand and push particles/chunks to places the
Potter/Ceramist doesn't want them to go - bloating!

Almost forgot - high-energy mixing may help to breakdown larger
chunks/trimmings to form a more homogeneous mixture. During firing, a larger
clumped mass of particles may be more influenced to move (bloat) by
surrounding low-viscosity molten liquid and gas pressure.

With regard to theory, bloating appears to be defined in terms of gas bubble
expansion.

Best wishes,

Jim Murphy

Michael Wendt on thu 17 jun 04


Des,
Thanks for the input. David has a problem that
only seems to occur with recycled clay so I thought
it might be gas bubbles that evolve due to organics.
Your clay body may be more porous than his even
though it appears to have zero absorption.
One thing is for sure, if a body does become
fully glassy early on, bubbles have no outlet to the
atmosphere and if the clay is very pyroplastic, the
expanding gas will exert enough force to cause a visible
bloat. I have posted an example of this effect.(see below)
I use seal strips over the top of the kiln shelves where
they meet under the damper in my updraft kiln.
The strips made with non-deaired clay did not show
any sign of bloating over many firings but now show
pronounced bloats while those that were deaired
extensively show none over hundreds of cone 10
firings. To see the effect, look at my web
site and check the clayart page.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
hit clayart button.
Des wrote:
I noticed that the centres of the cakes had bubbles about the
size of the bubbles in an "Aero" bar, so I nipped up the gland
packing bolts on the Mono pump, the sticking & splitting stopped
as did the "flummery". Point (finally) might be, the sucking in
a fine stream of air was causing the odd physical characteristics
of the clay by introducing fine bubbles. At no time did the clay
bloat in the firing, our body has zip absorption & porosity,
so maybe bubbles aren't the answer.
Des

Des & Jan Howard
Lue Pottery

Ivor and Olive Lewis on thu 17 jun 04


Dear David Baumee,
You say <tiny bloating event, due to water attack on felspar (or nepheline
syenite) particles by allowing an ion exchange to occur between H30+
ions in the water and Na+ or K+ in the felspar...>>'
That could be determined by doing the thermodynamic calculations for
the ion exchange reaction. Looking at the enthalpy values for the ions
concerned it would seem an unlikely event at room temperature, though
it is known that alkali metal ions can be stripped from felspar
minerals during weathering or other geological events. Without this,
where would we be for Clay?
Best regards,
Ivor Lewis.
Redhill,
S. Australia.

Michael Wendt on thu 17 jun 04


David,
I have been following this thread with interest.
I propose a set of controlled experiments to
get at the cause of the bloating.
1) Take fresh out of the bag porcelain and slice
it into thin sections. Label these and set them
out to dry completely. These are your control
chips. Each time you make a single change,
fire one of these controls in close proximity to
the chip for the idea being tested.
2) Take some additional slices of the clay fresh
from the bag and dry those. Slake some a short
time before drying to a usable state. Slake some
longer and some still longer. Label each test piece
with slake time. The goal of this test is to see if it is
slake time that causes the bloats.
3) Take some reclaim pots and repeat test 2 for
slake times. The goal of this test is to see if being
on the wheel is the culprit.
I raise this possibility because when we throw, we
add skin cells and bacteria to the clay. As these
decay, they produce microscopic gas bubbles.
Since the original clay is much
lower in these "seeds" of organic matter, the fresh
clay shows less tendency to bloat. In recycled clay,
aging lets the bubbles get bigger and during firing,
after the body has sealed but before it reaches final
cone, the gas bubbles continue to expand and result
in bloats.
If you lived nearer, it would be a simple matter to toss
50 lbs of your recycle porcelain into my deairing clay
mixer and run it at a high vacuum for 15-20 minutes
just before use to see if we could extract enough of the
bubbles to solve the bloating problem.
It is also possible that there are small bubbles in the
recycle clay just from the recycling process.
Stirring, screening and handling all introduce bubbles.
Unless a means for removing them is used, they can
result in bloats in porcelain.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com

John Kudlacek on fri 18 jun 04


Hi Sarah,
Never had the problem but then I haven't recycled much porcelain. I have
a couple of thoughts, perhaps naive, compared to the esoteria being
presented by others. For what they are worth, here they are: Could the
recycled porcelain contain (cultivate) organics which are not sufficiently
oxidized in the bisque? Could minute bits of plaster be getting into the
porcelain from the bats? In either case, don't know if these things could
cause bloating?
John in Topeka

David Beumee on fri 18 jun 04


Thanks to Michael Wendt, Jim Murphy and Ivor Lewis for your posts. I'll try my best to assimilate this info. Whew!

David Beumee
Earth Alchemy Pottery
Lafayette, CO


> David,
> I have been following this thread with interest.
> I propose a set of controlled experiments to
> get at the cause of the bloating.
> 1) Take fresh out of the bag porcelain and slice
> it into thin sections. Label these and set them
> out to dry completely. These are your control
> chips. Each time you make a single change,
> fire one of these controls in close proximity to
> the chip for the idea being tested.
> 2) Take some additional slices of the clay fresh
> from the bag and dry those. Slake some a short
> time before drying to a usable state. Slake some
> longer and some still longer. Label each test piece
> with slake time. The goal of this test is to see if it is
> slake time that causes the bloats.
> 3) Take some reclaim pots and repeat test 2 for
> slake times. The goal of this test is to see if being
> on the wheel is the culprit.
> I raise this possibility because when we throw, we
> add skin cells and bacteria to the clay. As these
> decay, they produce microscopic gas bubbles.
> Since the original clay is much
> lower in these "seeds" of organic matter, the fresh
> clay shows less tendency to bloat. In recycled clay,
> aging lets the bubbles get bigger and during firing,
> after the body has sealed but before it reaches final
> cone, the gas bubbles continue to expand and result
> in bloats.
> If you lived nearer, it would be a simple matter to toss
> 50 lbs of your recycle porcelain into my deairing clay
> mixer and run it at a high vacuum for 15-20 minutes
> just before use to see if we could extract enough of the
> bubbles to solve the bloating problem.
> It is also possible that there are small bubbles in the
> recycle clay just from the recycling process.
> Stirring, screening and handling all introduce bubbles.
> Unless a means for removing them is used, they can
> result in bloats in porcelain.
> Regards,
> Michael Wendt
> Wendt Pottery
> 2729 Clearwater Ave
> Lewiston, Idaho 83501
> USA
> wendtpot@lewiston.com
> www.wendtpottery.com
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.

Des & Jan Howard on fri 18 jun 04


Michael
Over the last couple of months filter cakes of our porcellaneous
stoneware body have been sticking to the cloths & peeling off
in thin sheets, the cakes have been splitting across as they are
being carried to the storage area & after non deair pugging have
a throwing texture that Trevor describes as "flummery",
I don't notice a difference, but then I'm not as picky.

I noticed that the centres of the cakes had bubbles about the
size of the bubbles in an "Aero" bar, so I nipped up the gland
packing bolts on the Mono pump, the sticking & splitting stopped
as did the "flummery". Point (finally) might be, the sucking in
a fine stream of air was causing the odd physical characteristics
of the clay by introducing fine bubbles. At no time did the clay
bloat in the firing, our body has zip absorption & porosity,
so maybe bubbles aren't the answer.
Des



Michael Wendt wrote:

> It is also possible that there are small bubbles in the
> recycle clay just from the recycling process.
> Stirring, screening and handling all introduce bubbles.
> Unless a means for removing them is used, they can
> result in bloats in porcelain.

--

Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au

mailtoandrew@FSMAIL.NET on sat 19 jun 04


Hello David,

I ve come into this thread rather late but you could do a lot worse the
get hold of the book Ceramic Faults And Their Remedies by Harry Fraser and
published by A & C Black in 1986. Its still in print and is available in
the US. Aimed at the studio potter its a easily understood guide to the
causes, and solutions, to many problems.

I cannt say that a case the same as your bloating problem is discussed as
the causes are legion and have been the subject of study for many years;
however it s a very useful reference.

Regards,

Andrew

Ivor and Olive Lewis on sun 20 jun 04


Dear John in Topeka,
Finely divided Calcium sulphate may be a serious contender, this is
because the decomposition of CaSO4 happens at a much higher
temperature than that of the carbonate. Another potential contaminant
in clay can be Iron Sulphide . Although in its massive form it is
black Iron sulphide could pass unnoticed if it passes a #220 screen
That residual of less that half a percent in a white firing clay could
be bothersome if it is not in the form of oxide or hydroxide.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.

mailtoandrew@FSMAIL.NET on tue 22 jun 04


Hello John and Ivor,

Im not sure about plaster being a potential contributor to bloating:

1. Plaster as either virgin material or old moulds is sometimes used as a
suspension aid, by increasing the viscocity, in slop fillers and fluxes.
2. To ease similar concerns expressed by my old boss at a former employer
I purposely contaminated a porcelain body with plaster. Being some years
ago I cannt remember the addition level but certainly a very significant
degree of contamination was shown to have not noticeable effect.

Perhaps a lump of plaster in a body could lead to localised problems; a
simple trial may be worth considering.

Regards,

Andrew

Earl Krueger on wed 23 jun 04


David,

Maybe it's not what is _in_ the recycled clay
body that is causing the bloating as much as
what is _not_ in the clay body.

You say you slake the dried clay in excess water.
What do you do with the excess water? Pour
it off? If so, what might you be dissolving and
removing with the extra water? This may be
why slake-time could be important.

Would be interesting to evaporate a quantity
of the waste water and see how much solid
material you recover.

I dunno. Maybe something here, maybe not.

Earl K...
Bothell, WA, USA

Ivor and Olive Lewis on wed 23 jun 04


Dear Andrew,
I am sure you are aware that the thermal decomposition of Calcium
Sulphate is a high temperature reaction which releases Sulphur
Trioxide gas. I would not expect this to happen during a bisque at ^06
but I would in a high firing stoneware or porcelain above ^8. The same
may also be true of Ferric Sulphide which is often present in some
ball clays.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.